Collisions and Change in Momentum

[jabbie3]

Homework Statement

A ball of mass 4.7 kg moving with speed of 1.9 m/s in the x-direction hits a wall and bounces back with the same speed in the -x-direction. What is the change of momentum of the ball? And in what direction?

Homework Equations

p=mv

The Attempt at a Solution

P=mv
P=4.7*1.9
P=8.93

 

[LowlyPion]

So what is the initial momentum?

What is the final momentum?

What is the difference?

 

[jabbie3]

The initial is 8.93 and the final is -8.93..so total momentum is 0? In what direction?

 

[KD-jay]

Try again using p_f - p_i to find the difference.

 

[LowlyPion]

The initial is 8.93 and the final is -8.93..so total momentum is 0? In what direction?

Sorry, signs matter.

Initial momentum = P
Final momentum = -P

Final - initial = Δ = (-P) - P = -2P

Negative because Δx/Δt is toward -x.